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I popped open one of my swamp coolers and in it there is a crusty white "dust" deposit everywhere, covering everything inside it. It also happens to be the unit where I haven't changed the filters in several years. Any guesses as to what happened there?

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  • as a note, black dust can be caused from the belt "shedding" as it were – rogerdpack Aug 2 '16 at 23:27
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That's just scale and mineral buildup. Evaporative coolers work by evaporating water; when they evaporate hard water that has minerals in it, the minerals stay behind. The better coolers have constant bleed lines or purge pumps to prevent this buildup by flushing it away. You can do it yourself by periodically draining all the water in the sump. Or you can install a bleed line or purge pump yourself.

But if you have one of the old coolers that uses thin aspen pads, know that you have to replace those pads at least every year. That type of older cooler requires a decent amount of maintenance; if you're not willing or able to do it, I would recommend replacing it with a newer unit that uses thick rigid media that lasts a long time instead of those aspen pads, and has a bleed line or purge pump to keep the scale buildup down.

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  • I also wonder if maybe some water was "spraying" around in there somehow, at one point...like a tiny leak or something... – rogerdpack Nov 13 '15 at 12:43
  • In the end I am getting this particular white dust build-up in "one swamp cooler but not another" on the same roof. If I had to guess it's because of proximity to a pine tree. Either tar or something else gets sucked in. The blades on the fan are also blackened sometimes with "something" and it's way messier than the other. It's a hypothesis anyway, might still be the belt somehow... – rogerdpack Nov 9 '20 at 4:15

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